This invention relates to a method of predicting the performance of certain electromagnetic devices based on the material properties of the electromagnetic core material used in the device, and in particular, to a method of predicting the performance of electric motors based on properties of the core material.
In the manufacture of certain electromagnetic devices such as motors, generators, transformers and the like, electrical grade steels are typically used for the electromagnetic core material. Steel grades specified as cold rolled motor lamination (CRML) steels are most commonly selected. CRML steels are typically relatively low in carbon content and relatively easy to stamp for making laminations.
It is standard practice in the industry today to specify electromagnetic core material based on the core loss and relative permeability of the material at an induced magnetic field of 1.5 Tesla (15 kilogauss). The problem with these standards is that the 1.5 Tesla relative permeability is not an accurate predictor of performance of the electromagnetic devices. In addition to being one of the most difficult characteristics to measure accurately due to the rapid drop off that occurs at the 1.5 Tesla level, theoretical investigation and experimentation have shown that the 1.5 Tesla relative permeability is not a significant factor in the performance of electromagnetic devices.
Relative permeability, particularly the 1.5 Tesla relative permeability, can vary somewhat from lot to lot of the given material made by a given process. This presents an additional problem because the 1.5 Tesla relative permeability cannot be tested until after the material is made and processed into a coil from which laminations can be stamped. The material manufacturer may be forced, at this point, to reject and scrap the coiled material if it is only slightly below the customer's 1.5 Tesla relative permeability specification. This potential for waste drives up material costs.
Because the performance of the finished device cannot be predicted even when the material produced satisfies the 1.5 Tesla relative permeability specification, manufacturers are required to fabricate prototypes of the finished device and then test the prototypes to verify the product's performance. This brings about the potential for further loss of the resources expended in making the device if the required performance goals are not met.
What is needed is a method of reliably predicting the performance of electromagnetic devices based on the magnetic characteristics of the electromagnetic core material. Such a method would be invaluable for motor manufacturers to design new motors and for material producers to design new alloys.